The present invention relates generally to an iterative decoder and, more particularly, to an iterative decoder in which data is improved after each decoding iteration.
In systems which communicate data through a channel from a transmitter to a receiver, it is known to code the data to be transmitted for a variety of reasons, though one of the primary reasons is usually to enhance its recovery by the receiver in spite of channel effects such as burst noise and ghosts resulting from multipath reception of the data. For example, a typical transmitter might interleave the data and convolutionally encode the interleaved data so that the data is less sensitive to burst noise and other signal impairments in the channel.
The receiver processes the data received from the channel usually in reverse order of the processing performed in the transmitter. Accordingly, a receiver decodes the data and then de-interleaves the decoded data. Some receivers are provided with iterative decoders that estimate the noise in the channel at each iteration with the objective that each noise estimation is intended to be better than the noise estimation from prior iterations. After a suitable number of iterations, the estimated noise is subtracted from the received signal and the received signal is then decoded to recover the transmitted data. It is noted that, in those prior art systems, the data itself is not improved by the iterations until after the final iteration when the estimated noise is removed from the received signal. By removing the noise from the received signal, it is hoped that the decoding can be performed more accurately.
The present invention is directed to an iterative decoder in which the data, instead of the noise estimation, is improved by the iterations.
In accordance with one aspect of the present invention, an iterative decoding system comprises first and second decoders. The first decoder decodes coded data, and the first decoder is arranged to reduce channel effects in the coded data to produce improved coded data. The second decoder decodes the improved coded data, and the second decoder is arranged to additionally reduce channel effects in the coded data.
In accordance with another aspect of the present invention, an iterative decoding system comprises first and second decoders and first and second data improvers. The first decoder decodes coded data. The first data improver reduces channel effects in the coded data based upon a reliability that the first decoder accurately decoded the encoded data so that the first data improver produces improved coded data. The second decoder decodes the improved coded data. The second data improver reduces channel effects in the improved coded data based upon a reliability that the second decoder accurately decoded the improved encoded data.
In accordance with still another aspect of the present invention, an encoding method comprises encoding un-coded data to produce first encoded data, encoding the un-coded data to produce second encoded data, and concatenating the un-encoded data, the first encoded data, and the second encoded data.